Selection Gradient

Age at first (α) and last (ω) breeding are important life-history traits; however, the direction and strength of selection detected on traits may vary depending on the fitness measure used. We provide the first estimates of lifetime breeding success (LBS) and λind (the population growth rate of an individual) of European badgers Meles meles, by genotyping 915 individuals, sampled over 18 years, for 22 microsatellites. Males are slightly larger than females, and the opportunity for selection was slightly greater for males, as predicted. λind and LBS both performed well in predicting the number of grand-offspring, and both detected selection for a late ω, until the age of eight. Differential selection (S′α) for an early α, however, was only detected using LBS, not with λind. In declining populations (λind < 1) selection favours reproduction later in life, whereas early reproduction is selected in increasing populations (λind > 1). As 41% of badgers were assigned only one offspring (λind < 1), whereas 40% were assigned more than two (λind > 1), this cancelled out S′α measured by λind.

Plants possess a remarkable capacity to alter their phenotype in response to the highly heterogeneous light conditions they commonly encounter in natural environments. In the present study with the weedy annual plant Sinapis arvensis, we (a) tested for the adaptive value of phenotypic plasticity in morphological and life history traits in response to low light and (b) explored possible fitness

Genetic and phenotypic variance/covariance matrices are a fundamental measure of the amount of variation and the pattern of association among traits for current investigations in evolutionary biology. Still, few methods have been developed to accomplish the goal of pinpointing in which traits two matrices differ most, hampering further works on the field. We here described a novel method for dissecting

The separation of nine un-ionized samples was studied as a function of temperature (T) and gradient steepness (b). Selectivity values Δlog α∗ were obtained for 160 compounds, ranging from nonpolar hydrocarbons to very polar drugs. Selectivity varied markedly with sample type: nonpolar compounds such as aromatic hydrocarbons and fatty acid methyl esters generally showed only modest changes in band spacing

We evaluated the diet of Common Barn-owls (Tyt0 alba) along an elevational gradient in Argentine Patagonia. Small mammals (mainly rodents) were the main prey accounting for 93.2% of total prey items. Consumption of rodents appeared to be dependent on their availability. Sizes of mam- malian prey were variable but most ranged from 10-100 g in body mass. We concluded that

Automation in colorectal mass detection is achieved as soon as the voxels representing colorectal masses can be automatically segmented. We tested the Hounsfield (HU) value in intensely contrast enhanced high-resolution CT colonography for automated segmentation of colorectal masses in 18 patients with 35 polyps (28 &lt; 10 mm, 7 &gt; or = 10 mm) and 7 carcinomas. Mean HU values of the colonic wall and masses were determined to deduce a gradient threshold for a segmentation process, which encodes the voxels bordering the colonic lumen with a colour ranging in intensity from 0 to 100% according to the selected gradient threshold range in the volume rendering. The results of the automated segmentation process were superimposed on a virtual double contrast and endoscopic display and validated through correlation with morphology. Mean HU values and their standard deviations for the colonic wall, polyps &lt; 10 mm, polyps &gt; or = 10 mm and carcinomas were 63 +/- 24, 154 +/- 38, 116 +/-...

The obligate mutualism between leafcutter ants and their Attamyces fungi originated 8 to 12 million years ago in the tropics, but extends today also into temperate regions in South and North America. The northernmost leafcutter ant Atta texana sustains fungiculture during winter temperatures that would harm the cold-sensitive Attamyces cultivars of tropical leafcutter ants. Cold-tolerance of Attamyces cultivars increases with winter harshness along a south-to-north temperature gradient across the range of A. texana , indicating selection for cold-tolerant Attamyces variants along the temperature cline. Ecological niche modeling corroborates winter temperature as a key range-limiting factor impeding northward expansion of A. texana . The northernmost A. texana populations are able to sustain fungiculture throughout winter because of their cold-adapted fungi and because of seasonal, vertical garden relocation (maintaining gardens deep in the ground in winter to protect them from extre...

Shell polymorphisms are widespread among those intertidal gastropods that lack a pelagic spreading stage. These polymorphisms may indicate diversifying selection in a heterogeneous habitat, but to do this the variation must be at least pardy inherited. Galician populations of Littorina saxatilis (Olivi) living in exposed rocky shores are highly polymorphic in several shell traits, e.g. ornamentation, banding and size. Mature snails of the upper-shore ridged and banded (RB) morph is, for example, often twice as large as mature individuals of the lower-shore smooth and unbanded (SU) morph of the same shore.We investigated the hypothesis that lower-shore snails grow more slowly and that differences in growth rate were at least partly inherited and could be explained by diversifying selection. We released snails of different origin (upper, mid- and lower shore) and morph (RB, SU and hybrids) at different shore levels and compared their shell increment after one month of growth. We found that despite considerable variation among individuals and among replicate samples (together about 53% of the total variation), average rates of growth differed between morphs. RB snails both from the upper and mid-shores grew at a high rate at all shore levels, SU snails grew considerably less, and hybrids grew at intermediate rates, at all levels. Inherited difference among morphs explained about 34% of the total variation while effects of shore levels and the interaction morph x shore level explained only 5 and 7%, respectively. Thus a large part of the difference in growth rate leading to different adult sizes of the two morphs has probably evolved due to spatially varying selection favouring large sizes in upper-shore and small sizes in lower-shore environments.